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From 0b7385ddaa538c5995d2f16333a80a0f579a6212 Mon Sep 17 00:00:00 2001
From: Stefan Hajnoczi <stefanha@redhat.com>
Date: Tue, 25 Mar 2014 14:23:46 +0100
Subject: [PATCH 39/49] dmg: prevent chunk buffer overflow (CVE-2014-0145)

RH-Author: Kevin Wolf <kwolf@redhat.com>
Message-id: <1395753835-7591-40-git-send-email-kwolf@redhat.com>
Patchwork-id: n/a
O-Subject: [virt-devel] [EMBARGOED RHEL-7.0 qemu-kvm PATCH 39/48] dmg: prevent chunk buffer overflow (CVE-2014-0145)
Bugzilla: 1079325
RH-Acked-by: Jeff Cody <jcody@redhat.com>
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>

From: Stefan Hajnoczi <stefanha@redhat.com>

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1079325
Upstream status: Embargoed

Both compressed and uncompressed I/O is buffered. dmg_open() calculates
the maximum buffer size needed from the metadata in the image file.

There is currently a buffer overflow since ->lengths[] is accounted
against the maximum compressed buffer size but actually uses the
uncompressed buffer:

switch (s->types[chunk]) {
case 1: /bin /boot /cgroup /dev /etc /home /lib /lib64 /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tmp /usr /var copy audio/ backends/ block/ bsd-user/ default-configs/ disas/ docs/ dtc/ fpu/ fsdev/ gdb-xml/ hw/ include/ ldscripts/ libcacard/ linux-headers/ linux-user/ net/ pc-bios/ pixman/ po/ qapi/ qga/ QMP/ qobject/ qom/ redhat/ roms/ scripts/ slirp/ stubs/ sysconfigs/ target-alpha/ target-arm/ target-cris/ target-i386/ target-lm32/ target-m68k/ target-microblaze/ target-mips/ target-moxie/ target-openrisc/ target-ppc/ target-s390x/ target-sh4/ target-sparc/ target-unicore32/ target-xtensa/ tcg/ tests/ trace/ ui/ util/
ret = bdrv_pread(bs->file, s->offsets[chunk],
s->uncompressed_chunk, s->lengths[chunk]);

We must account against the maximum uncompressed buffer size for type=1
chunks.

This patch fixes the maximum buffer size calculation to take into
account the chunk type. It is critical that we update the correct
maximum since there are two buffers ->compressed_chunk and
->uncompressed_chunk.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/dmg.c |   39 +++++++++++++++++++++++++++++++++------
 1 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/block/dmg.c b/block/dmg.c
index be0ee33..856402e 100644
--- a/block/dmg.c
+++ b/block/dmg.c
@@ -100,6 +100,37 @@ static int read_uint32(BlockDriverState *bs, int64_t offset, uint32_t *result)
     return 0;
 }
 
+/* Increase max chunk sizes, if necessary.  This function is used to calculate
+ * the buffer sizes needed for compressed/uncompressed chunk I/O.
+ */
+static void update_max_chunk_size(BDRVDMGState *s, uint32_t chunk,
+                                  uint32_t *max_compressed_size,
+                                  uint32_t *max_sectors_per_chunk)
+{
+    uint32_t compressed_size = 0;
+    uint32_t uncompressed_sectors = 0;
+
+    switch (s->types[chunk]) {
+    case 0x80000005: /* zlib compressed */
+        compressed_size = s->lengths[chunk];
+        uncompressed_sectors = s->sectorcounts[chunk];
+        break;
+    case 1: /* copy */
+        uncompressed_sectors = (s->lengths[chunk] + 511) / 512;
+        break;
+    case 2: /* zero */
+        uncompressed_sectors = s->sectorcounts[chunk];
+        break;
+    }
+
+    if (compressed_size > *max_compressed_size) {
+        *max_compressed_size = compressed_size;
+    }
+    if (uncompressed_sectors > *max_sectors_per_chunk) {
+        *max_sectors_per_chunk = uncompressed_sectors;
+    }
+}
+
 static int dmg_open(BlockDriverState *bs, QDict *options, int flags,
                     Error **errp)
 {
@@ -245,12 +276,8 @@ static int dmg_open(BlockDriverState *bs, QDict *options, int flags,
                     goto fail;
                 }
 
-                if (s->lengths[i] > max_compressed_size) {
-                    max_compressed_size = s->lengths[i];
-                }
-                if (s->sectorcounts[i] > max_sectors_per_chunk) {
-                    max_sectors_per_chunk = s->sectorcounts[i];
-                }
+                update_max_chunk_size(s, i, &max_compressed_size,
+                                      &max_sectors_per_chunk);
             }
             s->n_chunks += chunk_count;
         }
-- 
1.7.1